Chemical Compositions And Size Distributions Of Fine Particulate Matters Near A Typical Road In Beijing

It is of great importance to carry out systematic research on the sizedistributions and chemical compositions of fine particulate matters near themajor roads, which could help with the source apportionment of particles, theassessment of environmental impacts, the evaluation of human health risksand the decision-making of the pollution control from motor vehicles. In thisresearch, a typical road in Beijing was chosen and a comprehensiveobservation campaign was conducted in2008-2009. The concentrations ofPM mass, elements, inorganic ions and carbonaceous species weredetermined. The PM number concentration and the BC (black carbon)concentration were also measured. The mean PM0.2-2.5concentrations in thenon-Olympics periods were higher by60-90%compared with the WorldHealth Organization interim target-1level of PM2.5. Due to the temporarycontrol measures, the PM0.2-2.5mass concentrations during the Olympicsshowed a reduction rate of54%. The reduction rate of53%and63%wereobserved for the direct vehicle emission and the re-suspended dusts,respectively. Dust sources, anthropogenic sources and secondary formationprocesses were the main sources of the fine particles at roadside. Theanthropogenic sources contributed most to the particles in the smallest sizerange of0.2-0.5μm, whereas the dust sources contributed most to those inthe biggest size range of1.0-2.5μm. Compared with the city areas, vehicleemission was a more important contributor for PM2.5at roadside. Both theemission sources and the meteorological conditions could show significantinfluences on the PM size distributions and chemical compositions. The peaksat0.5-1.0μm in summer for PM mass were most likely attributed to strongersecondary formation processes, whereas the peaks at0.2-0.5μm in winter forPM mass were probably due to increased heating sources. The increasedsources also led to higher concentration of BC and increased concentration of Na, K, Cl, Br, Pb and Zn in the size range of0.2-0.5μm. The SO42-concentration peak of0.5-1.0μm in summer was most likely attributed toin-cloud processing. The number concentrations of the accumulation modeparticles were significantly influenced by meteorological factors, whereas theAitken mode particles showed a closer relationship with the traffic flow. Theaccumulation mode particles may come from regional pollution processes,while the Aitken mode particles may come from vehicle emissions. The BCconcentration was positively and negatively correlated with humidity andwind speed, respectively, and it was also significantly influenced by the airmass transfer processes. The BC concentrations showed a unimodal patternswith the peak in21:00-3:00, which was in line with the diurnal variation ofEC (elemental carbon) concentrations. The peak was related with the morestable weather conditions at the nighttime as well as the increase ofheavy-duty trucks. The emission of heavy-duty trucks was an importantsource for BC in the roadside and urban areas. The BC concentration in thebackground site was most significantly affected by the meteorological factorsbut had insigincant relationships with the traffic flow, which indicated thatBC in the background region might be formed by atmospheric transportationsand diffusions from the motor vehicle emissions in the roadside and urbanareas.